1. Field of the Invention
The present invention relates to the detection of signal transmission line integrity on differential signal transmission lines.
2. Prior art
Detection of open circuit and short circuit conditions on differential signal transmission lines has been done by obtaining manual access to the lines and imposing a signal on the lines to check conduction. It has been very difficult to reliably predict faults caused by opens and shorts based on data transmission monitoring as in U.S. Pat. No. 4,178,582 to Richman and U.S. Pat. No. 3,288,929 to Hutchinson. In a differential signal transmission bus, if one of the two transmission lines which are driven by a balanced current source driver and terminated by resistors to DC ground, is operational, at least half of the data signal transmitted is still received.
Such faults seriously degrade the performance of the differential signal transmission lines because they produce intermittent data errors which are hard to trace. The data errors require time to correct, either by error correction code, or retransmission due to parity checks.
Further, more costly alternatives to detect transmission line faults involve automatic superposition of special signals on the lines. A tool has also been used to detect shorts by plugging it into transceivers on the line in various orientations. This tool resulted in different lines being driven and sensed to detect shorts in the lines. This process has proven cumbersome and time consuming. These alternatives add to the cost, and potentially degrade performance.